The purpose of this study was to assess the direct effects of dobutamine on porcine coronary arteries and to investigate the mechanism of its action. Rings of coronary arteries from pigs were suspended in baths containing Krebs solution, and isometric tension was measured. The response to dobutamine (10(-8)-10(-3) M) was investigated in porcine coronary arterial rings contracted by KCl. The roles of endothelium, nitric oxide (NO), cyclic GMP (cGMP), prostaglandins and the adrenergic beta1, beta2-receptor on dobutamine-induced relaxation were also studied. Dobutamine inhibited the vasocontractivity to KCl and CaCl2, and relaxed porcine coronary artery. The relaxing response to dobutamine in coronary artery was significantly reduced by blockage of the adrenergic beta1-receptor, but not by removal of endothelium, blockage of the adrenergic beta2-receptor, inhibitors of nitric oxide synthase, guanylate cyclase and prostaglandin synthase. Our results suggest that dobutamine induces relaxation of isolated porcine coronary arteries via the adrenergic P1-receptor.